Array-processing Memes

When your manager says "just process the last 1000 files" but you're dealing with a PHP script that's about to iterate through 2 million files while comparing against a database of 1 million records. The script is literally pulling 1000 records with limit(1000) but then checking EACH of your 2 million files against those 1000 records with in_array() . That's a cool O(n²) operation that's going to take approximately checks notes forever to complete. Your server's CPU is already writing its resignation letter.